CD69-INDUCED MONOCYTE APOPTOSIS INVOLVES MULTIPLE NONREDUNDANT SIGNALING PATHWAYS

Simultaneous stimulation of human monocytes/macrophages or THP1 cells with LPS and an antibody specific for the activation marker CD69 induc es apoptosis. Here we demonstrate the involvement of multiple independ ent signals that are necessary for apoptosis induction, Thus, inhibito rs of phospholipase Az and lipoxygenase prevent apoptosis induction. S imilarly, the ADP-ribosylating G-protein-reactive pertussis toxin (PTX ) but not a mutant toxin lacking the ADP-ribosylating moiety (mPTX) pr events apoptosis induction. Furthermore, inhibition of NO generation a brogates completely the induction of apoptosis by LPS/CD69 ligation. T hese three pathways can be dissociated from each other in the sense th at interventions on the arachidonic acid metabolism or G proteins do n ot inhibit the generation of NO and that exogenous NO cannot reverse t he inhibition of cell death by inhibitors of phospholipase A(2) or PTX . In addition, both PTX and mPTX affect arachidonic acid mobilization only partially, indicating that the apoptosis-inhibitory effect of PTX (which is not shared by mPTX) cannot be explained by its effect on ph ospholipase A(2) activation. Both I,PS and anti-CD69 are sufficient on their own to activate cells, as determined by TNF production, NO gene ration, or arachidonic acid metabolism, but neither LPS nor anti-CD69 can induce apoptosis on their own. Thus, apoptosis induction in this s ystem involves at least three independent signal transduction systems- (i) arachidonic acid metabolism, (ii) NO, and (iii) PTX-sensitive even ts-each of which is necessary but insufficient to induce monocyte/macr ophage apoptosis. These findings underline the complex control of acti vation-induced apoptosis in cells of the myelomonocytic lineage. (C) 1 996 Academic Press, Inc.